Wave Power Conversion Research Articles

Research on a double float system for direct drive wave power conversion

The development and reasonable utilisation of wave energy have great realistic significance for solving environment pollution and energy crisis. A direct-drive system with no middle conversion devices such as gear and turbine, which has a simple structure and good stability, is widely applied to wave power systems. First, the study analysed the structure of a tubular permanent magnet linear generator. The structure of short primary and long secondary is chosen for wave power systems because of the convenience of installation and higher power density. Then, based on finite-element analysis, the structure of the generator is optimised by parametric analysis and genetic algorithm. A prototype is manufactured according to the optimised size, and the electromagnetic parameters are measured to verify the accuracy of simulation. Finally, a double floating direct-drive wave power system is installed in the port of Lian Yungang, China, and the system is tested by still and dynamic water; the results show that the system can effectively convert wave energy into electricity.

Towards innovative district energy management: a case study with stochastic renewable generators

The conversion of ocean wave power into sustainable electrical power represents a major opportunity to Nations endowed with such a kind of resource. At the present time the most of the technological innovations aiming at converting such resources are at early stage of development, with only a handful of devices close to be at the commercial demonstration stage. The Seaspoon device, thought as a large energy harvester, catches the kinetic energy of ocean waves with promising conversion efficiency, and robust technology, according to specific “wave-motion climate†. University of Genoa developed and patented a prototype to be deployed in medium average energy content seas (i.e. Mediterranean or Eastern Asia seas). This paper presents the installation phases of the first real scale prototype installed in the gulf of Genova and the monitoring of its performances. A brief description of the Seaspoon WEC is presented together with the monitoring equipment and procedures.In this research a thermoeconomic analysis of its integration in a real polygenerative district is also investigated. The impact of such this kind of stochastic renewable generator in the Savona Campus Smart Polygeneration Microgrid (SPM) is evaluated. The SPM plant is made up by (i) two auxiliary boilers (500kWth each), (ii) four micro gas turbines (30kWe, 2x65kWe and 100kWe), (iii) an internal combustion engine fed by natural gas (20kWe), (iv) an absorption chiller (100 kWf) and (v) PV panels for a total power installed of 100 kWe. Generators are “distributed†around the campus and they are coupled to electrical and thermal storages. Since the system is constituted by co-generative prime movers it can supply both electrical and thermal energy of the campus and the integration of storage is really important in order to follow both the requests, pursuing the best management strategy. The analysis of this smart-grid is performed exploiting a software developed by the Author's research group, which allows for the thermo-economic optimization of poly-generative energy systems. A model of the real plant was built and it was implemented in the software. The off-design curves of the real devices installed in the campus were used in order to increase the reliability of the simulation results. The grid was simulated considering the time dependent nature of the demands throughout the whole year. The model was used to simulate the smart grid behavior during the whole year, and find the best operational strategy. A time-dependent thermo-economic hierarchical approach has been used, considering the time-dependent electrical, thermal and cooling load demands during the year as problem constraints. The results are presented and discussed in depth and show the strong interaction between fossil and renewable resources, particularly the impact of unpredictable and randomized generators like the WECs ones. A dedicated model of the Seaspoon was implemented and exploited in the code.

Dynamic behavior of a wave power buoy with interior on-board linear generator

Wave energy conversion is attractive from the viewpoint of the size of the renewable resource, but prototypes continue to suffer from high costs, leading to the idea of combining a wave energy conversion function with a conventional function of another ocean or coastal infrastructure to achieve cost-sharing between functions. Here, a wave power device in which a linear generator is installed inside a sealed floating horizontal circular cylindrical buoy is studied, which has dual functions of a wave power converter and a floating breakwater. A two-dimensional Navier Stokes numerical wave tank is used, together with a Volume of Fluid method to model the detail of the buoy-wave interaction. After model validation, the primary conversion efficiency of the device, and the wave transmission and reflection coefficients are explored. It is found that the maximum primary conversion efficiency is close to 25%. In resonant state, the amplitude of the translator's relative oscillation could be much larger than that of incident wave. When the incident wave frequency departs from the natural frequency of the linear generator, the energy conversion efficiency deteriorates rapidly. When wave energy conversion reaches maximum efficiency, the corresponding wave transmission coefficients are in the range of 0.7–0.75, and the corresponding wave reflection coefficients are in the range of 0.2–0.3.

Hydrodynamic analysis and shape optimization for vertical axisymmetric wave energy converters

The absorber is known to be vertical axisymmetric for a single-point wave energy converter (WEC). The shape of the wetted surface usually has a great influence on the absorber’s hydrodynamic characteristics which are closely linked with the wave power conversion ability. For complex wetted surface, the hydrodynamic coefficients have been predicted traditionally by hydrodynamic software based on the BEM. However, for a systematic study of various parameters and geometries, they are too multifarious to generate so many models and data grids. This paper examines a semi-analytical method of decomposing the complex axisymmetric boundary into several ring-shaped and stepped surfaces based on the boundary discretization method (BDM) which overcomes the previous difficulties. In such case, by using the linear wave theory based on eigenfunction expansion matching method, the expressions of velocity potential in each domain, the added mass, radiation damping and wave excitation forces of the oscillating absorbers are obtained. The good astringency of the hydrodynamic coefficients and wave forces are obtained for various geometries when the discrete number reaches a certain value. The captured wave power for a same given draught and displacement for various geometries are calculated and compared. Numerical results show that the geometrical shape has great effect on the wave conversion performance of the absorber. For absorbers with the same outer radius and draught or displacement, the cylindrical type shows fantastic wave energy conversion ability at some given frequencies, while in the random sea wave, the parabolic and conical ones have better stabilization and applicability in wave power conversion.

The location of offshore wave power devices structures epifaunal assemblages

With large-scale development of offshore wave power conversion, artificial structures become more common in the open sea. To examine how wave power devices may be colonized by epifaunal organisms, 21 concrete foundations used for anchoring wave power generators were studied during two years, 2007 and 2008. The foundations were placed in two different clusters, located north and south within the Lysekil test site at the Swedish west coast. The degree to which early recruits covered the foundations and the succession of epibenthic communities were documented during two years. A succession in colonization over time was observed, with a higher degree of cover in the northern location. Furthermore, the northern location showed an increase in number of individuals, number of species and in Shannon-Wiener diversity in 2008. Dominant organisms on the foundations were the serpulid tubeworms (Pomatoceros triqueter) and barnacles (Balanus sp.). This comprehensive large-scale study about succession and colonization patterns on wave power foundations suggests that the location of wave energy devices affects colonization patterns. This gives indications on settlement patterns on already operating and planned offshore wave power parks further off the coasts.

Harnessing the waves [wave power

In 2012, an old portacabin was moved to Scotland's National Museum of Mining to provide a space for teaching children about renewable energy. But this wasn't any portacabin - it came from the University of Edinburgh and was ground zero for several wave power technology breakthroughs. Occupied by the team of Stephen Salter, pioneer of the 'duck' wave power converter, over a 30-year period, the portacabin spawned three companies. Together they contributed about £200m to the Scottish economy but have also shown the potential and pitfalls of a technology still looking to prove itself. Like the waves it's trying to harness, the industry has had its peaks and troughs. In the last 18 months, two big Scottish wave power companies have gone into administration - in November 2014 Pelamis Wave Power, which started in Salter's portacabin, and in October 2015 Aquamarine Power, whose `Oyster' device was being tested at the European Marine Energy Centre in Orkney. was a hugely gutting process. It was 17 years and 750 person years of engineering effort, says Pelamis founder Richard Yemm of his company's failure. The Scottish government, however, has a plan to kick-start the industry and prevent it from becoming another technology lost to foreign competitors. In February 2015 it established a public innovation company, Wave Energy Scotland, investing £14.3m over a 13-month period including acquiring some Pelamis assets.

Wave energy extraction by horizontal floating cylinders perpendicular to wave propagation

A two-dimensional numerical wave flume is established based on finite element and Volume of Fluid (VOF) methods for incompressible viscous flow. The numerical model is used to simulate waves interacting with single and double horizontal floating cylinders perpendicular to the direction of wave propagation. In the simulations, motion of the floating cylinders, wave forces and wave surface elevations in front of and behind the cylinders are calculated. By applying a damping force on the cylinders to simulate the electrical load, the primary conversion efficiency of wave power is derived. The effect of the cylinders’ cross-sectional size, the normalized damping coefficient for the cylinders’ heave motion, the primary conversion efficiency and the wave transmission coefficient are discussed. This investigation reveals that: larger cylinders are capable of extracting more wave power than smaller ones and also lowering wave transmission; an optimum normalized damping coefficient exists for wave power conversion; when this coefficient increases, heave motions of the cylinders decrease whilst the relative vertical wave force on the cylinders increases; total primary conversion efficiency for double cylinders is higher than that of two separately deployed cylinders due to cylinder-wise interaction.

Improvement of Performance of Wave Power Conversion Due to the Projecting Walls for Oscillating Water Column Type Wave Energy Converter

This paper describes a method to improve the performance of primary conversion of wave power takeoff. The wave energy converter (WEC) used here was of oscillating water column (OWC) type. This method for improvement has been already proposed in past research and its usefulness has been confirmed. It involves projecting walls (PWs) being attached to the front of the inlet–outlet of the OWC. The prediction method of hydrodynamic behaviors for the OWC type WEC with PWs installed is explained in this paper. The boundary element method with the Green's function is applied, and influence of air pressure and free surface within every air-chamber was directly taken into consideration in the prediction method based on linear potential theory. Validity of the prediction method was proved by comparing the results with the results of model experiments. Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation, and the efficiency of primary conversion of wave power were investigated. From the calculations, length of the PWs was shown to affect the efficiency of primary conversion. It was possible to equip the PWs so as to enable improvements in oblique waves to beam sea conditions as well as in the head sea conditions. This paper examined not only the PWs but also the application and effects of the end walls (EWs) with the slit. The EWs were very useful to improve the efficiency.

Parametric Study on a Caisson Based OWC Wave Energy Converting System

This study uses a numerical method to analyze the proposed model structure. Before the parametric analysis, a pre-analysis to make sure the analytical results are accountable, a verification analysis was performed. The results found are compared well with the limited experimental findings of Goda et al. and it is very encouraging to find that for the proposed method as an alternative for green energy developments, as long as an appropriate design is performed, an OWC combined with breakwater structure may provide an alternative for green energy system utilized in a harbor area. From the results of the first stage of parameter analysis that the size of the openings of the cell of converting system is variable, a traditional full opened cell is not necessary the most efficient design for the wave power conversion in terms of the variations of air pressure inside the cell and air speed through the outlet orifice that will drive the electricity power generator.

Development of a Simple and Innovative Wave Energy Harvester Suitable for Ocean Sensor Network Application

The article represents a new idea about an innovative, simple and cost effective marine energy harvester for powering offshore sensor nodes working as part of Ubiquitous Sensor Network (USN). Betterment of these aqua farms by including these into wireless sensor network so that they could be remote controlled from far land, is needed to make this offshore farming more popular. For this step to be done one major concern is the powering process of the sensor nodes used as the key part of sensing or monitoring purpose of the offshore projects. So our study focuses on the design and numerical study of a wave energy harvesting device for supplying uninterrupted electric power to offshore sensor nodes serving as part of ocean environment monitoring network or any marine aquaculture farm. Analysis of the environmental and device sizing factors that makes the efficiency to deviate, have been discussed here. It is a novel, floating type, double chambered wave energy converter that uses the Oscillating Water Column technology for conversion of wave power into electrical power.

Quantifying wave power and wave energy converter array production potential

Global wave energy inventories show that the West Coast of Canada possesses one of the most energetic wave climates in the world, with an annual wave energy flux of 40–50kW/m at the continental shelf. With this wave climate there is an opportunity to generate significant quantities of electricity through wave energy conversion (WEC) technologies. However, detailed knowledge of both the temporal and spatial distribution of both wave climate and energy production characteristics are missing precursors to the development of this regional wave energy opportunity.To quantify the gross wave energy resource along the West Coast of Vancouver Island, and hence the feasibility of deploying WEC technologies, a detailed Simulating WAves Nearshore (SWAN) numerical wave propagation model was developed. The SWAN model encompasses 410,000km2, covers 1500km of the Western Canadian coastline and the resolution is optimised by water depth and proximity to areas of high wave energy flux. The SWAN model hindcasts wave conditions for the 10year period, at a 3h temporal resolution. Independent validation of the SWAN model indicates a 0.92 correlation coefficient for significant wave heights and 0.80 for average wave periods.To translate the gross resource data into electricity generation estimates, novel methods to reveal high priority WEC farm deployment locations were implemented. Using generic WEC performance metrics, theoretical wave farm outputs were synthesized over a decade long time scale. Regional WEC farms were shown capable to providing up to 139.92GWh of energy to the electrical grid annually. The seasonality of the WEC generated electricity correlates well with the load demand within the region.This updated understanding of the wave climate and wave power production opportunity in Western Canada provides the necessary data to electrical utilities and policy makers to assess the opportunity benefits and costs associated with future WEC industry in Canada.

Optimal Design for High Output Power of Transverse-Flux-Type Cylindrical Linear Synchronous Generator

This paper presents an optimal design for achieving high output power in a transverse-flux-type cylindrical linear synchronous generator (TFC-LSM), especially for application in wave power conversion. We obtain optimal design by considering the number of salient poles in armature cores in the designated cross-sectional area. First, we describe the basic configuration of the transverse-flux-type cylindrical model used for design and proceed to explain three types of models with different numbers of salient poles. Second, we describe the optimal design process based on the practical rapid optimal design approach. Finally, we analyze the results of the optimal design of TFC-LSM.

Energy conversion of orbital motions in gravitational waves: Simulation and test of the Seaspoon wave energy converter

The conversion of ocean wave power into sustainable electrical power represents a major opportunity to Nations endowed with such a kind of resource. At the present time the most of the technological innovations aiming at converting such resources are at early stage of development, with only a handful of devices close to be at the commercial demonstration stage. The Seaspoon device, thought as a large energy harvester, catches the kinetic energy of ocean waves with promising conversion efficiency, and robust technology, according to specific “wave-motion climate”. University of Genoa aims to develop a prototype to be deployed in medium average energy content seas (i.e. Mediterranean or Eastern Asia seas). This paper presents the first simulation and experimental results carried out on a reduced scale proof-of-concept model tested in the laboratory wave flume.

Response and conversion efficiency of two degrees of freedom wave energy device

This paper concerns the response and efficiency of a two-body wave power conversion device. The physical problem of the device is simplified as a forced vibration system with viscous damping in two degrees of freedom. Based on the linear wave theory, wave excitation forces, added masses and damping are derived by use of an eigenfunction expansion matching method. The expressions of the response and efficiency are deduced from the motion equations of the device, and the optimal principle is presented as well. Numerical results indicate that damping optimal curve has a wave peak that is independent of the spring, and the value of the peak and the corresponding frequency are only related to the calculation conditions. Optimal curve presents two peaks when the spring exists, and the corresponding frequency width decreases with the increase of elastic coefficient. The damping is relative small at low frequency peak, while the response is relative high. The damping is relative high at high frequency optimization peak, while the response is relative small and almost smaller than the amplitude of the incident wave. With the decrease of the external damping coefficient, the relative motion amplitude and the efficiency increase, while the width of crest decreases.

Design of a New Oscillating Buoy Wave Power Generation Device

With the deepening of global energy crisis, looking for the new energy to replace traditional energy become the only way for the development of energy. This paper designs a new oscillating buoy ocean wave power generation device. It introduces the basic composition of the device and its structure, and its working principle and process. Combining the wave theory and calculation principle, wave power conversion efficiency theory, analysis and calculate the energy conversion efficiency of the device. Suppose the device is under the action of linear wave, through the theoretical calculation, the theoretical efficiency of this device is up to 0.383 when the wave period is 4 s, wave height is 0.5 m, buoy Side length is 0.3m, wind pipe diameter is 0.05. Compared with common wave power generation device, this device has higher power generation efficiency.

Numerical Simulation of Interactions between Waves and Pendulum Wave Power Converter

The interactions between waves and the pendulum wave power converter were simulated, considering Navier-Stokes (N-S) equations as governing equations of the fluid, using the k-ε turbulence model and finite element software ADINA. The setting wave-generating boundary method and viscosity damping region method were developed in the numerical wave tank. Nodal velocities were applied on each layer of the inflow boundary in the setting wave-generating boundary method. The viscosity of the fluid in the damping region was obtained artificially in the viscosity damping region method, and the energy in the fluid was decreased by the viscosity in governing equations. The physical model tests were simulated with the fluid-structure interaction (FSI) numerical model. The numerical results were compared with the experimental data, and then the results were discussed. A reference method is advanced to design the pendulum wave power converter. The method to solve the complex FSI problems is explored.

Wave power extraction by arbitrary arrays of non-diffracting oscillating water columns

A model to predict wave power conversion from arbitrary arrays of oscillating water columns is presented. Based on linear potential theory and idealized non-diffracting machines, it relies on a published analytical solution for the flow field generated by a single oscillating pressure patch on the ocean surface. Estimates of wave power conversion are obtained for several array configurations and well-defined wave resources at two sites in Hawaii, using a single-processor computer. Such results illustrate the versatility and computational efficiency of the model. The proposed approach allows a relatively easy evaluation of interferences among individual machines. This would be useful in optimizing the spatial arrangement of oscillating water columns in large wave farms.

Far-field theory of wave power capture by oscillating systems

A new derivation is given of an equation, relating the capture width of a wave power converter to the polar diagram of the waves generated by the device. The pattern of waves in the lee of the device is calculated in detail.

Simulation and Experimental Research of a Novel Vircator

A new configuration of an axially-extracted vircator with three resonant cavities is put forward and optimized by simulation with the PIC code. The output power of over 1 GW is obtained at around 4.1 GHz in the experiment, in agreement well with the PIC simulation results. The beam to wave power conversion efficiency is more than 6.6%.

파력발전용 횡류형 수력터빈의 성능 및 내부유동

Clean and renewable energy technologies using ocean energy give us non-polluting alternatives to fossil and nuclear-fueled power plants to meet establishment of countermeasures against the global warming and growing demand for electrical energy. Among the ocean energy resources, wave power takes a growing interest because of its enormous amount of potential energy in the world. Therefore, various types of wave power conversion system to capture the energy of ocean waves have been developed. However, suitable turbine type is not normalized yet because of relatively low efficiency of the turbine systems.<BR> The purpose of this study is to investigate the internal flow and performance characteristics of a cross-flow type hydro turbine, which will be built in a caisson for wave power generation. Numerical simulation using a commercial CFD code is conducted to clarify the effects of the turbine rotation speed and flow rate variation on the turbine characteristics. The results show that the output power of the cross-flow type hydro turbine with symmetric nozzle shape is obtained mainly from Stage 2. Turbine inlet configuration should be designed to obtain large amount of flow rate because the static pressure and absolute tangential velocity are influenced considerably by inlet flow rate.